Recently, a white-light emitting diode having near ultraviolet to blue-light emitting diode as an excitation source is actively studied. As a green phosphor, a β-Sialon phosphor activated by a rare earth element is reported in Patent Literature 1. The β-Sialon phosphor emits fluorescent light with green color of 525 to 545 nm by excitation with ultraviolet light of 315 nm or less, and a phosphor capable of emitting strong light in response to this excitation wavelength is in need. Meanwhile, Patent Literature 2 discloses a Sr3Al3Si13O2N21 phosphor activated by a rare earth element. With regard to such green-light emitting phosphor, emission of strong green fluorescent light by the aforementioned excitation wavelength is also in need.
The phosphor disclosed in Patent Literature 1 is, however, inappropriate for an application since the optimum excitation wavelength is present in an ultraviolet range. Meanwhile, Patent Literature 3 discloses a material capable of emitting strong green fluorescent light according to excitation of a β-Sialon phosphor by near ultraviolet to blue light. Accordingly, those phosphors can be used for vacuum fluorescent displays (VFDs), field emission displays (FEDs) plasma display panels (PDPs), cathode ray tubes (CRTs) white-light emitting diodes (LEDs), or the like, and their use as a phosphor having low luminance degradation is expected.